Electric power converter control device and process and converter comprising such a device

ABSTRACT

The control device of an electric power converter comprises a control device controlling turn-on of semi-conductor legs. The converter comprises a rectifier to supply a DC voltage on intermediate lines, a voltage filter connected on the intermediate lines, an inverter connected between said intermediate lines and an output, and a common neutral connection. The control device comprises a processing unit to supply modulation signals of control signals of said inverter legs. The control device controls a common leg comprising electronic power components connected between said intermediate lines and the common neutral connection. The processing unit controls said common leg according to a modulation signal of said common leg determined with a reference voltage setpoint.

BACKGROUND OF THE INVENTION

The invention relates to a control device of an electric power convertercomprising control means for controlling turn-on of the semi-conductorlegs, said electric power converter comprising:

-   -   rectifying means to receive an electric voltage or current input        and to supply a DC voltage on intermediate DC voltage lines,    -   DC voltage filtering means connected on said intermediate lines,    -   conversion means having at least two legs connected between said        DC voltage lines and outputs to convert said DC voltage into        output AC voltages, and    -   a common neutral or earth conductor connection between an input        and an output, said control means controlling turn-on of said        legs of the conversion means and comprising processing means to        supply modulation signals of control signals of said legs.

The invention also relates to such a converter comprising said controldevice and a control process of said converter.

STATE OF THE ART

Known electric power converters are used in particular inuninterruptible power supplies and speed regulators for electric motorsor associated with power generators for coupling to a power distributionsystem. Such a converter 1 represented in FIG. 1 generally comprises DCvoltage VDC lines L1 and L2 and an inverter 2 formed by two powersemi-conductor legs 2A, 2B, 2C connected between the lines L1 and L2 tosupply on output AC voltages VO to a load 3 or to an electric powerdistribution system. When the legs are controlled in high frequency, inparticular in pulse width modulation, electric filters 4 can be fittedbetween the outputs of the legs 2A, 2B, 2C and the load 3 or powersystem. Often a rectifier 5 connected between AC inputs VI and the linesL1 and L2 supplies the DC voltage VDC. Capacitors C1 and C2 connected tothe lines L1 and L2 perform filtering of the DC voltage VDC.

When the load is unbalanced, a neutral conductor has to be distributedon output to ensure correct voltages. In FIG. 2, the load comprises aneutral conductor LN connected to a mid-point of the filteringcapacitors C1 and C2. These capacitors generally have very highcapacitance values to ensure a good stability of the voltage even withvery strong neutral currents. A control device 6 controls thesemi-conductors of the legs to supply AC voltages referenced notablywith respect to the neutral conductor.

To increase the control level of the neutral current and voltage, inparticular in the case of over-modulation of control of the leg of theinverter 2, the neutral line LN can be connected to a fourth leg 2N ofthe inverter 2. In FIG. 3, the leg 2N is connected like the other legsbetween the DC voltage lines L1 and L2.

FIG. 4 shows an example of a part of a processing unit 7 of a controlcircuit 6 to supply control signals of the legs. In this circuit, aregulator 8 enables three-phase modulation signals to be regulated andsupplied according to reduced setpoints Cd, Cq, Co, notably by a Park orConcordia transformation in the domains dqo or αβo. These knowntransformations and rotations are generally computed by means ofmatrices respectively called Park and Concordia matrices. Signals MC1for each phase on output from the regulator are preferably used formodulation of intersecting type on a triangular high-frequency carriersignal enabling pulse width modulation. In the diagram of FIG. 4, theregulator 8 supplies first three-phase modulation signals MC1, a module9 determines over-modulation signals OM to be applied to the firstsignals MC1 with operators 10, a module 11 applies a reference voltageV2 to said signals MC1 by operators 12, and a module 13 supplies ahigh-frequency signal designed to be modulated by modulation signals MC2modified by the operators 10 and 12. Operators 14 combine the modulationsignals MC2 with preferably triangular high-frequency signals F1 tosupply control signals CVA, CVB and CVC of the inverter legs 2A, 2B, 2Cin pulse width modulation format. As the leg controls are preferablybinary on-off controls, a conditioning circuit 16 shapes the controlsignals. The over-modulation signals OM are generated by the modulationsignals MC1 and by the type of over-modulation. The reference signal V2is generally representative of a DC voltage, for example half thevoltage VDC of the lines L1 and L2.

FIG. 5 represents a known converter with common neutral or throughneutral. This converter used as an uninterruptible power supplycomprises a battery 17 connected via an adapter 18 to the DC voltagelines L1 and L2. In known manner, this converter comprises a rectifier19 with three legs 19A, 19B and 19C connected to AC voltages or currentinputs 20 and to the DC voltage VDC lines L1 and L2. A control circuit21 of the rectifier controls the rectifier legs according to the DCvoltage VDC and the currents to be taken from a power system connectedon input 20. The filtering capacitors have a common point connected tothe through neutral line LN. The voltage of the common point of thecapacitors is generally a mid-point voltage between the lines L1 and L2the value whereof is regulated by voltage-regulating semi-conductors T1and T2 controlled by a regulation control circuit 22. In this figure, aninverter of the same type as that of FIG. 2 is connected on the lines L1and L2 and to the mid-point of the capacitors.

In converters without a mid-point on the capacitors, in particular inthe three-phase or three-phase plus independent neutral converters ofFIGS. 1 and 3, the capacitors do not need to be of very high capacitancevalues. In the converters of the type of that of FIG. 2, when theneutral is connected to a common point of the capacitors C1 and C2, thevalue of the capacitors is high to absorb the neutral currents withoutdisturbing the DC voltage VDC too much. However, in converters with athrough neutral LN between inputs connected to a rectifier and outputsof an inverter as that of FIG. 5, the value and size of the filteringcapacitors C1 and C2 can become very high. The high values of thecapacitors are due in particular to the filtering and to absorption ofthe neutral currents of the load supplied by the inverter and theneutral currents of the source supplying the rectifier. High capacitancevalues of the capacitors in this case enable an independence between thestructures of the inverter and those of the rectifier to be ensured.Thus, strong neutral currents on the inverter side have littledisturbance effects on the rectifier or on the source currents.

Known state-of-the-art devices with through neutral such as that of FIG.5 have very high capacitor capacitance values which imply veryconsiderable costs when the converter power is high. In addition, insuch a converter, coupling of the neutral currents does not enable thepower in the semi-conductors to be reduced by over-modulation on thecontrols of the inverter and rectifier legs when the currents areunbalanced. The lack of over-modulation in the controls causes a powerloss on switching of the semi-conductors and imposes a higher DC voltageand a lower electrical efficiency of the converter. Fitting additionalneutral legs for the four-arm inverter and rectifier is not possiblewith a through neutral as known control devices do not enable neutralcurrents of the inverter and rectifier to be controlled in sufficientlyindependent manner to limit coupling between the rectifier, the inverterand the DC voltage lines.

SUMMARY OF THE INVENTION

The object of the invention is to provide a control device and processof an electric power converter and a converter comprising such a deviceenabling the problems of state-of-the-art converters with throughneutral to be overcome.

In a control device according to the invention:

-   -   said control means control a common leg comprising electronic        power components connected between said intermediate DC voltage        lines and the common connection, and    -   said processing means comprise means for determining a general        control component for processing an over-modulation,    -   said processing means controlling said common leg according to a        modulation signal of said common leg determined with a reference        voltage setpoint having a value representative of a voltage        between said intermediate lines and of a signal representative        of said general control component.

In a preferred embodiment:

-   -   the control means control legs of the conversion means, legs of        the rectifying means, and the common leg,    -   the processing means supplying modulation signals of each leg        according to signals representative of a reference voltage        setpoint, and    -   said modulation signals modulating carrier signals of the same        nature for each leg.

Preferably, the signals representative of reference voltage are the samefor determining modulation signals of each modulated leg of theconverter and the carrier signals are the same for determining controlsignals of each leg of the converter.

Advantageously, the processing means comprise means for determining ageneral control component for processing an over-modulation, saidgeneral control component being determined according to first modulationsignals of the legs of the conversion means, and one and the same signalrepresentative of the general control component is used to processmodulation signals of the legs of the conversion means and a modulationsignal of the common leg.

Advantageously, the processing means use a signal representative of thegeneral control component to process modulation signals of the legs ofthe rectifying means.

In a particular embodiment, the processing means comprise correctionmeans to correct said general control component according to signalsrepresentative of saturation of first modulation signals of therectifying means.

Advantageously, the correction means comprise means for forecastingsaturation values and means for reducing a signal representative of thegeneral control component according to said saturation values.

An electric power converter according to an embodiment of the inventioncomprises:

-   -   rectifying means to receive an electric voltage or current on        inputs and to supply a DC voltage on intermediate DC voltage        lines,    -   DC voltage filtering means connected on the intermediate lines,    -   conversion means having at least two legs connected between said        DC voltage lines and outputs to convert said DC voltage into        output AC voltages,    -   a common neutral conductor, ground or earth connection between        an input and an output,    -   control means to control turn-on of the legs of said conversion        means and comprising processing means to supply modulation        signals of control signals of said legs, and    -   a common leg comprising electronic power components connected        between said intermediate DC voltage lines and the common        connection and a control device as defined above to control said        common leg according to a modulation signal of said common leg        determined with a reference voltage setpoint.

Advantageously, said processing means supply modulation signals of thelegs of the conversion means representative of voltages different fromthe corresponding voltages of the input voltages of the rectifyingmeans.

Advantageously, said processing means supply modulation signals of thelegs of the conversion means having a fundamental frequency differentfrom the fundamental frequency of the input voltage of the rectifyingmeans.

Advantageously, said processing means supply modulation signals of thelegs of the conversion means having phases different from the phases ofthe input voltage of the rectifying means.

Advantageously, said control means of the control device control turn-onof the legs of said conversion means and of the legs of the rectifyingmeans in reversible manner, outputs to a load becoming power inputs, theconversion means becoming rectifying means, and the inputs becomingoutputs to supply AC electric power.

A control process according to the invention of an electric powerconverter comprising:

-   -   rectifying means to receive an electric input voltage or current        and to supply a DC voltage on intermediate DC voltage lines,    -   DC voltage filtering means connected on the intermediate lines,    -   conversion means having at least two legs connected between said        DC voltage lines and outputs to convert said DC voltage into        output AC voltages,    -   a common neutral conductor, ground or earth connection between        an input and an output,    -   a common leg comprising electronic power components connected        between said intermediate DC voltage lines and the common        connection, and    -   control means controlling turn-on of the legs of said conversion        means and comprising processing means to supply modulation        signals of control signals of said legs,        said process comprising:    -   a first step of determining first modulation signals for        controlling legs of the conversion means,    -   a first application step to apply a reference voltage setpoint        to a modulation signal of the common leg and to modulation        signals for controlling legs of the conversion means,    -   a second step of determining a general control component value,        and    -   a second application step to apply said general control        component to said common leg modulation signal and to modulation        signals for control of legs of the conversion means.

Preferably, the process comprises a third application step to apply areference voltage setpoint and a general control component valuesetpoint to modulation signals for control of legs of the rectifyingmeans.

Advantageously, the process comprises a detection step of saturation ofmodulation signals for control of legs of the rectifying means, and acorrection step of the general control component value according todetection of saturation of modulation signals of legs of the rectifyingmeans.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from thefollowing description of particular embodiments of the invention, givenas non-restrictive examples only and represented in the accompanyingdrawings in which:

FIGS. 1 to 3 represent diagrams of converters with inverters of knowntypes;

FIG. 4 represents a block diagram of a control device of known type;

FIG. 5 represents a diagram of a converter with through neutral of knowntype;

FIG. 6 represents a diagram of a converter according to an embodiment ofthe invention;

FIGS. 7 to 9 represent block diagrams of alternative embodiments of aprocessing unit of control devices according to an embodiment of theinvention;

la FIG. 10 represents a block diagram of a correction module of ageneral control component for a control device according to anembodiment of the invention;

la FIG. 11 represents a flowchart according to an example of a processaccording to the invention;

la FIG. 12 illustrates a type of over-modulation signal applicable to ageneral control component;

FIGS. 13A to 13C represent modulation signals comprising a generalcontrol component in a control device according to an embodiment of theinvention;

FIG. 14 represents rectifier leg control saturation signals; and

FIGS. 15A to 15C, 16A to 16C and 17A to 17C illustrate examples ofsignals showing general control component correction.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The electric power converter represented in FIG. 6 comprises:

-   -   a rectifier 19 to receive an electric voltage VI or current on        inputs 20 and to supply a DC voltage VDC on intermediate DC        voltage lines L1 and L2,    -   DC voltage filtering capacitors C1 and C2 connected on the        intermediate lines,    -   conversion means such as an inverter 2 having at least two legs        2A, 2B and 2C connected between said DC voltage lines L1 and L2        and outputs 30 to convert said DC voltage into output AC        voltages VO,    -   a common neutral conductor N or reference connection LN, and    -   a control device 31 controlling turn-on of the legs 2A, 2B, 2C        of said conversion means 2 and comprising a processing circuit 7        to supply modulation signals MC2 of control signals CVA, CVB,        CVC of said legs.

In this electric power converter according to an embodiment of theinvention, the converter comprises a common leg 32 comprising electronicpower components 32A and 32B connected between said intermediate DCvoltage VDC lines L1 and L2 and the common neutral connection LN. Theadditional common leg 32 enables the neutral currents to be controlledenabling an additional control level in order to reduce the size of thecapacitors. Advantageously, the neutral currents flowing in thisadditional leg also enable controlled over-modulation to be introducedand the voltage of the DC voltage line to be reduced to reduce losses byswitching. The control device 31 controls said common leg 32 accordingto a modulation signal MCom of said common leg determined with areference voltage setpoint V2. The common leg modulation signal MCommodulates a carrier signal F1 that is preferably close to or similar toa carrier signal F1 used for control of the inverter legs and of therectifier legs.

The reference voltage setpoint V2 for modulation signals of the commonleg is preferably close to or similar to reference voltage setpoints V2for modulation signals of legs of the inverter 2 and rectifier 19.

Thus, control of the common leg, control of the inverter legs andcontrol of the rectifier legs have the same carrier signal F1 andreference voltage setpoint V2 bases. With such bases, the modulationsignals representative of the rectifier input voltage and the inverteroutput voltage can be independent as the neutral currents able to flowin the common leg are synchronized by the carrier signal F1. In thiscase, even with a through neutral, the characteristics of the inputpower system voltages and currents can be different from thecharacteristics of the inverter output voltages. For example, the outputvoltage VO of the inverter can have a different voltage value from thevoltage VI of the input power system, but also a different phase or adifferent frequency.

In a particular embodiment of the invention, this converter with throughneutral can also operate in reversible manner. In this case, the controldevice controls turn-on of the inverter legs and rectifier legs inreversible manner. Outputs to a load then become power inputs, theinverter becomes a rectifier, and the inputs become outputs to supply ACelectric power.

FIG. 7 represents a block diagram of a processing unit 7 of a controlcircuit 6 of a control device according to an embodiment of theinvention. The control device is designed in particular to controlturn-on of legs of semi-conductors of an electric power converteraccording to FIG. 6.

The control circuit controls turn-on of the inverter legs 2A, 2B, 2C andcomprises a processing unit 7 to supply modulation signals MC2A, MC2Band MC2C of control signals CVA, CVB, CVC of said legs.

According to an embodiment of the invention, the control circuitcontrols a common leg 32 comprising electronic power components 32A and32B connected in series between said intermediate DC voltage VDC linesL1 and L2 and connected to the common neutral connection LN by theircommon mid-point. The processing unit modulates said common legaccording to a modulation signal Mcom determined with a referencevoltage setpoint V2. The common leg modulation signal Mcom is combinedin an operator 33 to modulate a carrier signal F1.

In the diagram of FIG. 7, a regulator 8 supplies first three-phasemodulation signals MC1A, MC1B and MC1C of the inverter 2, and a secondregulator 34 supplies first three-phase modulation signals MR1A, MR1B,MR1C of the rectifier 19. The first inverter modulation signals arecombined in operators 12 with a reference voltage setpoint V2 to supplysecond modified inverter modulation signals respectively MC2A, MC2B,MC2C. The first rectifier modulation signals are combined in operators35 with a reference voltage setpoint V2 to supply second modifiedrectifier modulation signals respectively MR2A, MR2B, MR2C. The modifiedmodulation signals MR1A, MR1B, MR1C and MC2A, MC2B, MC2C are combined inoperators respectively 14 and 36 to modulate carrier signals F1. Formodulation of the inverter legs, the rectifier legs and the common leg,the setpoint V2 applied to the operators 12, 35, 33 is of the samenature and the carrier F1 applied to the operators 14, 36 and 33 is ofthe same nature. Advantageously, the same voltage V2 is applied to theoperators 12, 35 and 33, and/or the same carrier signal F1 is applied tothe operators 14, 36 and 33. Modulated signals CVA, CVB, CVC aredesigned for control of the inverter legs, modulated signals CRA, CRB,CRC are designed for control of the rectifier legs and a signal Ccom isdesigned for control of the common leg.

Modulation of the signals is preferably in pulse width modulationmodulated for example in the operators 14, 36 and 33 according to amethod called intersecting.

FIG. 8 represents a block diagram of a control circuit 6 of a controldevice with an over-modulation function. In this diagram, a module 9receives the first inverter modulation signals MC1A, MC1B, MC1C suppliedby the regulator and determines a general control component OMcomprising over-modulation and control signals of the common leg 32.This component OM is combined with the first inverter modulation signalsMC1A, MC1B, MC1C in operators 10 and combined with the reference voltagesetpoint signal V2 in an operator 37 to supply a common leg modulationsignal MCom.

To prevent disturbances of the neutral currents, a signal representativeof the general control component is also applied for processing of therectifier modulation signals. But, as the voltages, frequencies andphases can be different between the input and output of the converterand the voltage of the intermediate DC voltage must remain limited so asnot to increase the dissipated power, there is a risk of saturation ofthe leg control signals. Thus, the control device of FIG. 9 comprises asaturation detection module 38. The module 38 receives the firstrectifier leg modulation signals MR1A, MR1B, MR1C and a first generalcontrol component signal OM0. The module 38 detects a risk of saturationand corrects the general control component signal OM0 according to anovershoot of a limit saturation value. On output of the module 38, a newcorrected general control component signal OM1 is combined with thefirst inverter leg modulation signals in operators 10, with the firstrectifier leg modulation signals MR1A, MR1B, MR1C in operators 39, andwith the reference voltage signal V2 in an operator 37 for control ofthe common leg. Preferably, the inverter leg modulation signals are alsocombined in operators 12 with the reference voltage signal V2 and inoperators 14 with a carrier signal F1, and the rectifier leg modulationsignals are also combined in operators 35 with the reference voltagesignal V2 and in operators 36 with a carrier signal F1. The operator 37supplies a common leg modulation signal Mcom resulting from thecorrected general control component OM1 and from the reference voltagesignal V2. The signal Mcom is combined with the carrier signal in theoperator F1.

FIG. 10 represents an example of a block diagram of a general controlcomponent correction module 38. Said general control component iscorrected according to signals representative of saturation of themodulation signals of the rectifying means. The module 38 comprisessaturation value determination modules 41, 42, 43 respectively SA, SB,SC for each rectifier leg modulation signal. The modules 41, 42, 43receive on input the first rectifier modulation signals respectivelyMR1A, MR1B, MR1C and the first general control component signal OM0 andsupply saturation value signals respectively SA, SB, SC on output. If arisk of saturation is detected, the first general control componentsignal and the saturation overshoot value signals SA, SB, SC arecombined in an operator 44 to correct the first general controlcomponent signal and to supply a new signal, or a new value OM1 of ageneral control component. For example, the modules 41, 42, and 43determine or forecast saturation values SA, SB, SC and the operator 44reduces a signal representative of the general control component OM1according to said saturation values.

In a device according to an embodiment of the invention, the generalcontrol component, the carrier signal and/or the reference voltagesignal are common to all the processing of the inverter legs, therectifier legs and the common leg. However, the processing unit cansupply inverter leg modulation signals having different voltages fromthe corresponding voltages of the rectifier input voltages and/orinverter leg modulation signals having a different fundamental frequencyfrom the fundamental frequency of the rectifier input voltage and/orinverter leg modulation signals having different phases from the phasesof the rectifier input voltage.

FIG. 11 represents an example of a flowchart of a control process of anelectric power converter according to the invention. The processcomprises a first determination step 60 of determining modulationsignals MC1A, MC1B, MC1C for control of the inverter legs. Then, asecond determination step 61 determines a general control componentvalue OM0 according to the first inverter modulation signals andpossibly to the type of over-modulation selected. In a step 62, a valuerepresentative of said general control component is applied to saidinverter and common leg modulation signals. A step 63 enables areference voltage setpoint V2 to be applied to the inverter legmodulation signals MC1A, MC1B, MC1C and to a common leg modulationsignal Mcom. A third determination step 64 determines modulation signalsfor rectifier leg control according to a reference voltage setpoint V2and to a general control component value OM.

In this flowchart, a saturation management phase 65 comprises generalcontrol component correction steps in case of risks of saturation of therectifier leg control. In this phase, a detection step 66 detects a riskof saturation of general control component modulation signals of therectifier leg control, a step 67 determines a saturation overshoot valueVsat by evaluating said overshoot of a first value of the generalcontrol component OM0 with a limit saturation value Vmax. Then acorrection step 68 corrects the general control component value OMaccording to detection of saturation Vsat of rectifier leg modulationsignals. If saturations are not detected, the general control componentOM is not corrected and a step 69 applies the first value of the generalcontrol component OM0 to the component OM.

FIG. 12 represents a type of inverter leg modulation and over-modulationsignals applicable to a general control component. Signals MCA, MCB, MCCare three-phase signals comprising a flat over-modulation 70 on the sinewave peak. The general control component signal OM is determinedaccording to the modulation signals MCA, MCB, MCC. In this case, thisgeneral component OM compensates over-modulation to restore a sine waveshape by low level modulation on the other legs.

FIG. 13A shows modulation signals MC2A, MC2B, MC2C to modulate inverterleg control. FIG. 13B shows general control component signals OMgenerated according to the inverter modulation signals that havepriority. FIG. 13C represents rectifier leg modulation signals MR2A,MR2B, MR2C also comprising an over-modulation but whose voltage formsare not synchronised with those of the inverter. On the non-priorityrectifier modulation signals not playing a part in constituting thegeneral control component, saturations 71 may occur.

FIG. 14 represents signals showing an example of rectifier leg controlsaturation. The modulation signals MR2A, MR2B and MR2C are alsorepresentative of the rectifier voltage input signals. When themodulation signals exceed a limit saturation value Vmax a risk ofsaturation 71 is possible. The voltage Vmax, is also representative ofor depends on the voltage of the DC voltage VDC lines or the referencevoltage V2. Saturation values can be defined by the difference betweenthe limit value Vmax and the values of the first rectifier legmodulation signals MR1A, MR1B and MR1C.

To reduce or eliminate this saturation risk, the general controlcomponent can advantageously be corrected in particular according to thesaturation values. FIG. 15A shows a first general control component OM0determined according to first inverter modulation signals MC1A, MC1B,MC1C. FIG. 15B shows an example of saturation value signals Vsatdetermined according to the first general control component OM0 and thefirst rectifier leg modulation signals MR1A, MR1B and MR1C. FIG. 15Cshows a second general control signal OM1 corrected according to thesaturation value signals.

FIG. 16A shows inverter leg modulation signals MC2A, MC2B, MC2Ccomprising over-modulation corrected with a corrected second generalcontrol component signal OM1. An example of the form of a correctedsecond general control component signal OM1 is represented in FIG. 16B.FIG. 16C shows corrected modulation signals MR2A, MR2B, MR2C limited toa maximum value Vmax according to correction of the general controlcomponent. FIGS. 17A to 17C represent signals equivalent to the signalsof the corresponding FIGS. 16A to 16C. In FIG. 17A, the signal MC2Acomprises a clipped part 75 corresponding to correction of the generalcontrol component OM1. In FIG. 17B, the general control component signalOM1 comprises a clipped part 76 corresponding to correction to eliminateor reduce the effects of saturation risks. FIG. 17C shows in detail alimited part of the modulation signal MR2A of a rectifier leg.

Conversion devices according to embodiments of the invention can inparticular be uninterruptible power supplies, speed regulators,uni-directional or bi-directional power converters between two electricpower distribution systems able to have very different electricalcharacteristics, or frequency converters. The common neutral line LN canbe connected to an earth conductor depending on the types of powersystems or installation protective devices. This connection LN canitself be a ground or earth conductor or a common reference line betweenthe converter input and output.

The semi-conductors of these converters are advantageously insulatedgate transistors called IGBT but other types of semi-conductors can beused. The legs can comprise several semi-conductors connected in seriesand/or in parallel depending on the voltages, currents or electricpowers used. For example, the input or output voltages can range from afew tens of volts to a thousand volts for low-voltage systemapplications or have voltages of several thousand volts in particular inmedium voltage applications. The input or output currents can range froma few amperes to more than a thousand amperes.

Another application of a converter according to the invention can beelectric power transformation, in particular for replacement of mediumvoltage—low voltage, low voltage—low voltage or medium voltage—mediumvoltage transformers.

In an other technical language the legs of the converter can be namedarms.

1. Control device of an electric power converter comprising controlmeans for controlling turn-on of the semi-conductor legs, said electricpower converter comprising: rectifying means to receive an inputelectric voltage or current and to supply a DC voltage on intermediateDC voltage lines, DC voltage filtering means connected on theintermediate lines, conversion means having at least two legs connectedbetween said DC voltage lines and outputs to convert said DC voltageinto output AC voltages, and a common neutral or earth conductorconnection between an input and an output, said control meanscontrolling turn-on of said legs of the conversion means and comprisingprocessing means to supply modulation signals of control signals of saidlegs, control device wherein: said control means control a common legcomprising electronic power components connected between saidintermediate DC voltage lines and the common connection, and saidprocessing means comprise means for determining a general controlcomponent for processing an over-modulation, said processing meanscontrolling said common leg according to a modulation signal of saidcommon leg determined with a reference voltage setpoint having a valuerepresentative of a voltage between said intermediate lines and of asignal representative of said general control component.
 2. Deviceaccording to claim 1 wherein: the control means control legs of theconversion means, legs of the rectifying means, and the common leg, theprocessing means supplying modulation signals of each leg according tosignals representative of a reference voltage setpoint, and saidmodulation signals modulating carrier signals of the same nature foreach leg.
 3. Device according to claim 2 wherein the signalsrepresentative of reference voltage are the same for determiningmodulation signals of each modulated leg of the converter and thecarrier signals are the same for determining control signals of each legof the converter.
 4. Device according to claim 2 wherein the processingmeans comprise means for determining a general control component forprocessing an over-modulation, said general control component beingdetermined according to first modulation signals of the legs of theconversion means, and one and the same signal representative of thegeneral control component is used to process modulation signals of thelegs of the conversion means and a modulation signal of the common leg.5. Device according to claim 4 wherein the processing means use a signalrepresentative of the general control component to process modulationsignals of the legs of the rectifying means.
 6. Device according toclaim 5 wherein the processing means comprise correction means tocorrect said general control component according to signalsrepresentative of saturation of first modulation signals of therectifying means.
 7. Device according to claim 6 wherein the correctionmeans comprise means for forecasting saturation values and means forreducing a signal representative of the general control componentaccording to said saturation values.
 8. Electric power convertercomprising: rectifying means to receive an electric voltage or currenton inputs and to supply a DC voltage on intermediate DC voltage lines,DC voltage filtering means connected on the intermediate lines,conversion means having at least two legs connected between said DCvoltage lines and outputs to convert said DC voltage into output ACvoltages, a common neutral conductor, ground or earth connection betweenan input and an output, and control means to control turn-on of the legsof said conversion means and comprising processing means to supplymodulation signals of control signals of said legs, converter comprisinga common leg comprising electronic power components connected betweensaid intermediate DC voltage lines and the common connection and acontrol device according to claim 1 to control said common leg accordingto a modulation signal of said common leg determined with a referencevoltage setpoint.
 9. Converter according to claim 8 wherein saidprocessing means supply modulation signals of the legs of the conversionmeans representative of voltages different from the correspondingvoltages of the input voltages of the rectifying means.
 10. Converteraccording to claim 8 wherein said processing means supply modulationsignals of the legs of the conversion means having a differentfundamental frequency from the fundamental frequency of the inputvoltage of the rectifying means.
 11. Converter according to claim 8wherein said processing means supply modulation signals of the legs ofthe conversion means having different phases from the phases of theinput voltage of the rectifying means.
 12. Converter according to claim8 wherein said control means of the control device control turn-on ofthe legs of said conversion means and of the legs of the rectifyingmeans in reversible manner, outputs to a load becoming power inputs, theconversion means becoming rectifying means, and the inputs becomingoutputs to supply AC electric power.
 13. Control process of an electricpower converter comprising: rectifying means to receive an electricinput voltage or current and to supply a DC voltage on intermediate DCvoltage lines, DC voltage filtering means connected on the intermediatelines, conversion means having at least two legs connected between saidDC voltage lines and outputs to convert said DC voltage into output ACvoltages, a common neutral conductor, ground or earth connection betweenan input and an output, a common leg comprising electronic powercomponents connected between said intermediate DC voltage lines and thecommon connection, and control means controlling turn-on of the legs ofsaid conversion means and comprising processing means to supplymodulation signals of control signals of said legs, said processcomprising: a first step of determining first modulation signals forcontrolling legs of the conversion means, a first application step toapply a reference voltage setpoint to a modulation signal of the commonleg and to modulation signals for controlling legs of the conversionmeans, a second step of determining a general control component value,and a second application step to apply said general control component tosaid common leg modulation signal and to modulation signals for controlof legs of the conversion means.
 14. Process according to claim 13comprising: a third application step to apply a reference voltage and ageneral control component value setpoint to modulation signals forcontrol of legs of the rectifying means.
 15. Process according to claim14 comprising: a detection step of saturation of modulation signals forcontrol of legs of the rectifying means, and a correction step of thegeneral control component value according to detection of saturation ofmodulation signals of legs of the rectifying means.